Palisade endings: cholinergic sensory organs or effector organs?
OBJECTIVE
This study aims to complement the authors' prior findings on palisade endings in extraocular muscles (EOMs) of monkeys, and to clarify whether palisade endings are cholinergic motor or cholinergic sensory.


METHODS
Macaque monkeys (Macaca fascicularis, n = 10) of both sexes were analyzed using three-dimensional (3D) reconstructions, confocal laser scanning microscopy (CLSM), and conventional/immuno transmission electron microscopy (TEM). For CLSM, we used three combinations of triple fluorescent labeling. EOM wholemounts were labeled with cholinergic markers, including choline acetyltransferase (ChAT), choline transporter (ChT), vesicular acetylcholine transporter (VAChT), and a classical postsynaptic marker for motor terminals, namely alpha-bungarotoxin. Muscle fibers were counterstained with phalloidin. 3D reconstructions were done of triple-labeled palisade endings. For immuno TEM, tissue was labeled with antibody against ChAT.


RESULTS
Concordant with prior findings, the authors demonstrated that palisade endings at the muscle fiber tips arose from nerve fibers that are ChAT-positive. In 25% of the cases, axons forming palisade endings established multiple neuromuscular contacts outside the palisade complex. Such additional neuromuscular contacts were motor terminals, as demonstrated by alpha-bungarotoxin binding. All palisade endings established nerve terminals on the tendon. In 40% of the palisade endings, nerve terminals were observed on the muscle fiber as well. Neurotendinous contacts and neuromuscular contacts in palisade endings were ChT/ChAT/VAChT-immunoreactive. Neuromuscular contacts exhibited structural features of motor terminals and were also alpha-bungarotoxin positive.


CONCLUSIONS
The present study ascertained that palisade endings are cholinergic motor organs. Therefore, it was concluded that palisade endings are not candidates to provide eye-position signals.
Blumer
Roland
R
Center of Anatomy and Cell Biology, Medical University Vienna, Vienna, Austria. roland.blumer@meduniwien.ac.at
Konakci
Kadriye Zeynep
KZ
Pomikal
Christine
C
Wieczorek
Grazyna
G
Lukas
Julius-Robert
JR
Streicher
Johannes
J
D000818:Animals; D002038:Bungarotoxins / Q000378:metabolism; D002795:Choline O-Acetyltransferase / Q000378:metabolism*; D005260:Female; D008252:Macaca fascicularis; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D016253:Microscopy, Immunoelectron; D009046:Motor Neurons / Q000378:metabolism* / Q000648:ultrastructure; D009411:Nerve Endings / Q000378:metabolism* / Q000648:ultrastructure; D009412:Nerve Fibers / Q000378:metabolism* / Q000648:ultrastructure; D009469:Neuromuscular Junction / Q000378:metabolism* / Q000648:ultrastructure; D009801:Oculomotor Muscles / Q000294:innervation*; D010590:Phalloidine / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000378:metabolism; D050494:Vesicular Acetylcholine Transport Proteins / Q000378:metabolism
D002038:Bungarotoxins; D026901:Membrane Transport Proteins; D050494:Vesicular Acetylcholine Transport Proteins; C065637:choline transporter; D010590:Phalloidine; D002795:Choline O-Acetyltransferase